Independent Submission M. Blanchet
Request for Comments: 5572 Viagenie
Category: Experimental F. Parent
ISSN: 2070-1721 Beon Solutions
February 2010
IPv6 Tunnel Broker with the Tunnel Setup Protocol (TSP)
Abstract
A tunnel broker with the Tunnel Setup Protocol (TSP) enables the
establishment of tunnels of various inner protocols, such as IPv6 or
IPv4, inside various outer protocols packets, such as IPv4, IPv6, or
UDP over IPv4 for IPv4 NAT traversal. The control protocol (TSP) is
used by the tunnel client to negotiate the tunnel with the broker. A
mobile node implementing TSP can be connected to both IPv4 and IPv6
networks whether it is on IPv4 only, IPv4 behind a NAT, or on IPv6
only. A tunnel broker may terminate the tunnels on remote tunnel
servers or on itself. This document describes the TSP within the
model of the tunnel broker model.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This is a contribution to the RFC Series, independently
of any other RFC stream. The RFC Editor has chosen to publish this
document at its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5572.
IESG Note
The content of this RFC was at one time considered by the IETF, and
therefore it may resemble a current IETF work in progress or a
published IETF work.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
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RFC 5572 Tunnel Setup Protocol (TSP) February 20101. Introduction
This document first describes the TSP framework, the protocol
details, and the different profiles used. It then describes the
applicability of TSP in different environments, some of which were
described in the v6ops scenario documents.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Description of the TSP Framework
Tunnel Setup Protocol (TSP) is a signaling protocol to set up tunnel
parameters between two tunnel endpoints. TSP is implemented as a
tiny client code in the requesting tunnel endpoint. The other
endpoint is the server that will set up the tunnel service. TSP uses
XML [W3C.REC-xml-2004] basic messaging over TCP or UDP. The use of
XML gives extensibility and easy option processing.
TSP negotiates tunnel parameters between the two tunnel endpoints.
Parameters that are always negotiated are:
o Authentication of the users, using any kind of authentication
mechanism (through Simple Authentication and Security Layer (SASL)
[RFC4422]) including anonymous
o Tunnel encapsulation:
* IPv6 over IPv4 tunnels [RFC4213]
* IPv4 over IPv6 tunnels [RFC2473]
* IPv6 over UDP-IPv4 tunnels for NAT traversal
o IP address assignment for the tunnel endpoints
o DNS registration of the IP endpoint address (AAAA)
Other tunnel parameters that may be negotiated are:
o Tunnel keep-alive
o IPv6 prefix assignment when the client is a router
o DNS delegation of the inverse tree, based on the IPv6 prefix
assigned
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
o Routing protocols
The tunnel encapsulation can be explicitly specified by the client,
or can be determined during the TSP exchange by the broker. The
latter is used to detect the presence of NAT in the path and select
IPv6 over UDP-IPv4 encapsulation.
The TSP connection can be established between two nodes, where each
node can control a tunnel endpoint.
The nodes involved in the framework are:
1. the TSP client
2. the client tunnel endpoint
3. the TSP server
4. the server tunnel endpoint
1,3, and 4 form the tunnel broker model [RFC3053], where 3 is the
tunnel broker and 4 is the tunnel server (Figure 1). The tunnel
broker may control one or many tunnel servers.
In its simplest model, one node is the client configured as a tunnel
endpoint (1 and 2 on the same node), and the second node is the
server configured as the other tunnel endpoint (3 and 4 on the same
node). This model is shown in Figure 2:
_______________
| TUNNEL BROKER |--> Databases (DNS)
| |
| TSP |
| SERVER |
|_______________|
| |
__________ | | ________
| | | | | |
| TSP |--[TSP]-- +---------| |
| CLIENT | | TUNNEL |--[NETWORK]--
[HOST]--| |<==[CONFIGURED TUNNEL]==>| SERVER |
|___________| | |
|________|
Figure 1: Tunnel Setup Protocol Used on Tunnel Broker Model
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
___________ ________
| | | TSP |
| TSP |-----------[TSP]---------| SERVER |
| CLIENT | | |--[NETWORK]--
[HOST]--| |<==[CONFIGURED TUNNEL]==>| TUNNEL |
|___________| | SERVER |
|________|
Figure 2: Tunnel Setup Protocol Used on Tunnel Server Model
From the point of view of an operating system, TSP is implemented as
a client application that is able to configure network parameters of
the operating system.
2.1. NAT Discovery
TSP is also used to discover if a NAT is in the path. In this
discovery mode, the client sends a TSP message over UDP, containing
its tunnel request information (such as its source IPv4 address) to
the TSP server. The TSP server compares the IPv4 source address of
the packet with the address in the TSP message. If they differ, one
or many IPv4 NATs are in the path.
If an IPv4 NAT is discovered, then IPv6 over UDP-IPv4 tunnel
encapsulation is selected. Once the TSP signaling is done, the
tunnel is established over the same UDP channel used for TSP, so the
same NAT address-port mapping is used for both the TSP session and
the IPv6 traffic. If no IPv4 NAT is detected in the path by the TSP
server, then IPv6 over IPv4 encapsulation is used.
A keep-alive mechanism is also included to keep the NAT mapping
active.
The IPv4 NAT discovery builds the most effective tunnel for all
cases, including in a dynamic situation where the client moves.
2.2. Any Encapsulation
TSP is used to negotiate IPv6 over IPv4 tunnels, IPv6 over UDP-IPv4
tunnels, and IPv4 over IPv6 tunnels. IPv4 over IPv6 tunnels is used
in the Dual-Stack Transition Mechanism (DSTM) together with TSP
[DSTM].
2.3. Mobility
When a node moves to a different IP network (i.e., change of its IPv4
address when doing IPv6 over IPv4 encapsulation), the TSP client
reconnects automatically to the broker to re-establish the tunnel
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
(keep-alive mechanism). On the IPv6 layer, if the client uses user
authentication, the same IPv6 address and prefix are kept and re-
established, even if the IPv4 address or tunnel encapsulation type
changes.
3. Advantages of TSP
o Tunnels established by TSP are static tunnels, which are more
secure than automated tunnels [RFC3964]; no third-party relay
required.
o Stability of the IP address and prefix, enabling applications
needing stable address to be deployed and used. For example, when
tunneling IPv6, there is no dependency on the underlying IPv4
address.
o Prefix assignment supported. Can use provider address space.
o Signaling protocol flexible and extensible (XML, SASL)
o One solution to many encapsulation techniques: IPv6 in IPv4, IPv4
in IPv6, IPv6 over UDP over IPv4. Can be extended to other
encapsulation types, such as IPv6 in IPv6.
o Discovery of IPv4 NAT in the path, establishing the most optimized
tunneling technique depending on the discovery.
4. Protocol Description4.1. Terminology
Tunnel Broker: In a tunnel broker model, the broker is taking charge
of all communication between tunnel servers (TSs) and tunnel
clients (TCs). Tunnel clients query brokers for a tunnel and the
broker finds a suitable tunnel server, asks the tunnel server to
set up the tunnel, and sends the tunnel information to the tunnel
Client.
Tunnel Server: Tunnel servers are providing the specific tunnel
service to a tunnel client. It can receive the tunnel request
from a tunnel broker (as in the tunnel broker model) or directly
from the tunnel client. The tunnel server is the tunnel endpoint.
Tunnel Client: The tunnel client is the entity that needs a tunnel
for a particular service or connectivity. A tunnel client can be
either a host or a router. The tunnel client is the other tunnel
endpoint.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
v6v4: IPv6-over-IPv4 tunnel encapsulation
v6udpv4: IPv6-over-UDP-over-IPv4 tunnel encapsulation
v4v6: IPv4-over-IPv6 tunnel encapsulation
4.2. Topology
The following diagrams describe typical TSP scenarios. The goal is
to establish a tunnel between tunnel client and tunnel server.
4.3. Overview
The Tunnel Setup Protocol is initiated from a client node to a tunnel
broker. The Tunnel Setup Protocol has three phases:
Authentication phase: The Authentication phase is when the tunnel
broker/server advertises its capability to a tunnel client and
when a tunnel client authenticate to the broker/server.
Command phase: The command phase is where the client requests or
updates a tunnel.
Response phase: The response phase is where the tunnel client
receives the request response from the tunnel broker/server, and
the client accepts or rejects the tunnel offered.
For each command sent by a tunnel client, there is an expected
response from the server.
After the response phase is completed, a tunnel is established as
requested by the client. If requested, periodic keep-alive packets
can be sent from the client to the server.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xF | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSP data |
...
Figure 7: TSP Header for Reliable UDP
The 4-bit field (0-3) is set to 0xF. This marker is used by the
tunnel broker to identify a TSP signaling packet that is sent
after an IPv6 over UDP is established. This is explained in
Section 4.5.2
Sequence Number: 28-bit field. Set by the tunnel client. Value is
increased by one for every new packet sent to the tunnel broker.
The return packet from the broker contains the unaltered sequence
number.
Timestamp: 32-bit field. Set by the tunnel client. Generated from
the client local-time value. The return packet from the broker
contains the unaltered timestamp.
TSP data: Same as in the TCP/v4 case. Content described in later
sections.
The TSP client builds its UDP packet as described above and sends it
to the tunnel broker. When the tunnel broker responds, the same
values for the sequence number and timestamp MUST be sent back to the
client. The TSP client can use the timestamp to determine the
retransmission timeout (current time minus the packet timestamp).
The client SHOULD retransmit the packet when the retransmission
timeout is reached. The retransmitted packet MUST use the same
sequence number as the original packet so that the server can detect
duplicate packets. The client SHOULD use exponential backoff when
retransmitting packets to avoid network congestion.
4.4.2. Authentication Phase
The authentication phase has 3 steps:
o Client's protocol version identification
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
o Server's capability advertisement
o Client authentication
When a TCP or UDP session is established to a tunnel broker, the
tunnel client sends the current protocol version it is supporting.
The version number syntax is:
VERSION=2.0.0 CR LF
Version 2.0.0 is the version number of this specification. Version
1.0.0 was defined in earlier documents.
If the server doesn't support the protocol version, it sends an error
message and closes the session. The server can optionally send a
server list that may support the protocol version of the client.
Example of an unsupported client version (without a server list):
-- Successful TCP Connection --
C:VERSION=0.1 CR LF
S:302 Unsupported client version CR LF
-- Connection closed --
Figure 8: Example of Unsupported Client Version
Example of a version not supported (with a server list):
-- Successful TCP Connection --
C:VERSION=1.1 CR LF
S:1302 Unsupported client version CR LF
<tunnel action="list" type="broker">
<broker>
<address type="ipv4">1.2.3.4</address>
</broker>
<broker>
<address type="dn">ts1.isp1.com</address>
</broker>
</tunnel>
-- Connection closed --
Figure 9: Example of Unsupported Client Version, with Server
Redirection
If the server supports the version sent by the client, then the
server sends a list of the capabilities supported for authentication
and tunnels.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
CAPABILITY TUNNEL=V6V4 TUNNEL=V6UDPV4 AUTH=ANONYMOUS AUTH=PLAIN
AUTH=DIGEST-MD5 CR LF
Tunnel types must be registered with IANA and their profiles are
defined in Section 7. Authentication is done using SASL [RFC4422].
Each authentication mechanism should be a registered SASL mechanism.
Description of such mechanisms is not in the scope of this document.
The tunnel client can then choose to close the session if none of the
capabilities fit its needs. If the tunnel client chooses to
continue, it authenticates to the server using one of the advertised
mechanisms using SASL. If the authentication fails, the server sends
an error message and closes the session.
The example in Figure 10 shows a failed authentication where the
tunnel client requests an anonymous authentication that is not
supported by the server.
Note that linebreaks and indentation within a "C:" or "S:" are
editorial and not part of the protocol.
-- Successful TCP Connection --
C:VERSION=2.0.0 CR LF
S:CAPABILITY TUNNEL=V6V4 AUTH=DIGEST-MD5 CR LF
C:AUTHENTICATE ANONYMOUS CR LF
S:300 Authentication failed CR LF
Figure 10: Example of Failed Authentication
Figure 11 shows a successful anonymous authentication.
-- Successful TCP Connection --
C:VERSION=2.0.0 CR LF
S:CAPABILITY TUNNEL=V6V4 TUNNEL=V6UDPV4 AUTH=ANONYMOUS AUTH=PLAIN
AUTH=DIGEST-MD5 CR LF
C:AUTHENTICATE ANONYMOUS CR LF
S:200 Success CR LF
Figure 11: Successful Anonymous Authentication
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
Digest-MD5 authentication with SASL follows [RFC2831]. Figure 12
shows a successful digest-MD5 SASL authentication.
-- Successful TCP Connection --
C:VERSION=2.0.0 CR LF
S:CAPABILITY TUNNEL=V6V4 TUNNEL=V6UDPV4 AUTH=ANONYMOUS AUTH=PLAIN
AUTH=DIGEST-MD5 CR LF
C:AUTHENTICATE DIGEST-MD5 CR LF
S:cmVhbG09aGV4b3Msbm9uY2U9MTExMzkwODk2OCxxb3A9YXV0aCxhbGdvcml0aG09bWQ
1LXNlc3MsY2hhcnNldD11dGY4
C:Y2hhcnNldD11dGY4LHVzZXJuYW1lPSJ1c2VybmFtZTEiLHJlYWxtPSJoZXhvcyIsbm9
uY2U9IjExMTM5MDg5NjgiLG5jPTAwMDAwMDAxLGNub25jZT0iMTExMzkyMzMxMSIsZG
lnZXN0LXVyaT0idHNwL2hleG9zIixyZXNwb25zZT1mOGU0MmIzYzUwYzU5NzcxODUzZ
jYyNzRmY2ZmZDFjYSxxb3A9YXV0aA==
S:cnNwYXV0aD03MGQ1Y2FiYzkyMzU1NjhiZTM4MGJhMmM5MDczODFmZQ==
S:200 Success CR LF
Figure 12: Successful Digest-MD5 Authentication
The base64-decoded version of the SASL exchange is:
S:realm="hexos",nonce="1113908968",qop="auth",algorithm=md5-sess,
charset=utf8
C:charset=utf8,username="username1",realm="hexos",nonce="1113908968",
nc=00000001,cnonce="1113923311",digest-uri="tsp/hexos",
response=f8e42b3c50c59771853f6274fcffd1ca,qop=auth
S:rspauth=70d5cabc9235568be380ba2c907381fe
Once the authentication succeeds, the server sends a success return
code and the protocol enters the Command phase.
4.4.3. Command and Response Phase
The Command phase is where the tunnel client sends a tunnel request
or a tunnel update to the server. In this phase, commands are sent
as XML messages. The first line is a "Content-length" directive that
indicates the size of the following XML message. When the server
sends a response, the first line is the "Content-length" directive,
the second is the return code, and third one is the XML message, if
any. The "Content-length" is calculated from the first character of
the return code line to the last character of the XML message,
inclusively.
Spaces can be inserted freely.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
parameters and indicates its acceptance of the keep-alive period
(Section 4.6). Finally, the client sends an accept message to the
server.
Once the accept message has been sent, the server and client
configure their tunnel endpoint based on the negotiated tunnel
parameters.
4.5. Tunnel Establishment4.5.1. IPv6-over-IPv4 Tunnels
Once the TSP signaling is complete, a tunnel can be established on
the tunnel server and client node. If a v6v4 tunnel has been
negotiated, then an IPv6-over-IPv4 tunnel [RFC4213] is established
using the operating system tunneling interface. On the client node,
this is accomplished by the TSP client calling the appropriate OS
commands or system calls.
4.5.2. IPv6-over-UDP Tunnels
If a v6udpv4 tunnel is configured, the same source/destination
address and port used during the TSP signaling are used to configure
the v6udpv4 tunnel. If a NAT is in the path between the TSP client
and the tunnel broker, the TSP signaling session will have created a
UDP state in the NAT. By reusing the same UDP socket parameters to
transport IPv6, the traffic will flow across the NAT using the same
state.
+------+-----------+--------+
| IPv4 | UDP | IPv6 |
| hdr. | port 3653 | |
+------+-----------+--------+
Figure 14: IPv6 Transport over UDP
At any time, a client may re-establish a TSP signaling session. The
client disconnects the current tunnel and starts a new TSP signaling
session as described in Section 4.4.1.2. If a NAT is present and the
new TSP session uses the same UDP mapping in the NAT as for the
tunnel, the tunnel broker will need to disconnect the client tunnel
before the client can establish a new TSP session.
4.6. Tunnel Keep-Alive
A TSP client may select to send periodic keep-alive messages to the
server in order to maintain its tunnel connectivity. This allows the
client to detect network changes and enable automatic tunnel
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
re-establishment. In the case of IPv6-over-UDP tunnels, periodic
keep-alive messages can help refresh the connection state in a NAT if
such a device is in the tunnel path.
For IPv6-over-IPv4 and IPv6-over-UDP tunnels, the keep-alive message
is an ICMPv6 echo request [RFC4443] sent from the client to the
tunnel server. The IPv6 destination address of the echo message MUST
be the address from the 'keepalive' element sent in the tunnel
response during the TSP signaling (Section 4.4.3). The echo message
is sent over the configured tunnel.
The tunnel server responds to the ICMPv6 echo requests and can keep
track of which tunnel is active. Any client traffic can also be used
to verify if the tunnel is active. This can be used by the broker to
disconnect tunnels that are no longer in use.
The broker can send a different keep-alive interval from the value
specified in the client request. The client MUST conform to the
broker-specified keep-alive interval. The client SHOULD apply a
random "jitter" value to avoid synchronization of keep-alive messages
from many clients to the server [FJ93]. This is achieved by using an
interval value in the range of [0.75T - T], where T is the keep-alive
interval specified by the server.
4.7. XML Messaging
This section describes the XML messaging used in the TSP signaling
during the command and response phase. The XML elements and
attributes are listed in the DTD (Appendix A).
4.7.1. Tunnel
The client and server use the tunnel token with an action attribute.
Valid actions for this profile are: 'create', 'delete', 'info',
'accept', and 'reject'.
create: action used to request a new tunnel or update an existing
tunnel. Sent by the tunnel client.
delete: action used to remove an existing tunnel from the server.
Sent by the tunnel client.
info: action used to request current properties of an existing
tunnel. This action is also used by the tunnel broker to send
tunnel parameters following a client 'create' action.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
accept: action used by the client to acknowledge the server that the
tunnel parameters are accepted. The client will establish a
tunnel.
reject: action used by the client to signal the server that the
tunnel parameters offered are rejected and no tunnel will be
established.
The tunnel 'lifetime' attribute is set by the tunnel broker and
specifies the lifetime of the tunnel in minutes. The lifetime is an
administratively set value. When a tunnel lifetime has expired, it
is disconnected on the tunnel server.
The 'tunnel' message contains three elements:
<client>: Client's information
<server>: Server's information
<broker>: List of other servers
4.7.2. Client Element
The 'client' element contains 3 sub-elements: 'address', 'router',
and 'keepalive'. These elements are used to describe the client
request and will be used by the server to create the appropriate
tunnel. The client element is the only element sent by a client.
The 'address' element is used to identify the client IP endpoint of
the tunnel. When tunneling over IPv4, the client MUST send only its
IPv4 address to the server. When tunneling over IPv6, the client
MUST only send its IPv6 address to the server.
The broker then returns the assigned IPv6 or IPv4 address endpoint
and domain name inside the 'client' element when the tunnel is
created or updated. If supported by the broker, the 'client' element
MAY contain the registered DNS name for the address endpoint assigned
to the client.
Optionally, a client MAY send a 'router' element to ask for a prefix
delegation.
Optionally, a client MAY send a 'keepalive' element that contains the
keep-alive time interval requested by the client.
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RFC 5572 Tunnel Setup Protocol (TSP) February 20104.7.3. Server Element
The 'server' element contains two elements: 'address' and 'router'.
These elements are used to describe the server's tunnel endpoint.
The 'address' element is used to provide both IPv4 and IPv6 addresses
of the server's tunnel endpoint, while the 'router' element provides
information for the routing method chosen by the client.
4.7.4. Broker Element
The 'broker' element is used by a tunnel broker to provide an
alternate list of brokers to a client in the case where the server is
not able to provide the requested tunnel.
The 'broker' element contains an 'address' element or a series of
'address' elements.
5. Tunnel Request Examples
This section presents multiple examples of requests.
5.1. Host Tunnel Request and Reply
A simple tunnel request consist of a 'tunnel' element that contains
only an 'address' element. The tunnel action is 'create', specifying
a 'v6v4' tunnel encapsulation type. The response sent by the tunnel
broker is an 'info' action. Note that the registered Fully-Qualified
Domain Name (FQDN) of the assigned client IPv6 address is also
returned to the tunnel client.
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RFC 5572 Tunnel Setup Protocol (TSP) February 20105.3. IPv4 over IPv6 Tunnel Request
This is similar to the previous 'create' action, but with the tunnel
type is set to 'v4v6'.
-- Successful TCP Connection --
C:VERSION=1.0 CR LF
S:CAPABILITY TUNNEL=V4V6 AUTH=DIGEST-MD5 AUTH=ANONYMOUS
CR LF
C:AUTHENTICATE ANONYMOUS CR LF
S:OK Authentication successful CR LF
C:Content-length: 228 CR LF
<tunnel action="create" type="v4v6">
<client>
<address type="ipv6">
2001:db8:0c18:ffff:0000:0000:0000:0001
</address>
</client>
</tunnel> CR LF
Figure 17: Simple Tunnel Request Made by a Client
If the allocation request is accepted, the broker will acknowledge
the allocation to the client by sending a 'tunnel' element with the
attribute 'action' set to 'info', 'type' set to 'v4v6' and the
'lifetime' attribute set to the period of validity or lease time of
the allocation. The 'tunnel' element contains 'server' and 'client'
elements.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
S: Content-length: 370 CR LF
200 OK CR LF
<tunnel action="info" type="v4v6" lifetime="1440">
<server>
<address type="ipv4" length="30">
192.0.2.2
</address>
<address type="ipv6">
2001:db8:c18:ffff:0000:0000:0000:0002
</address>
</server>
<client>
<address type="ipv4" length="30">
192.0.2.1
</address>
<address type="ipv6">
2001:db8:c18:ffff::0000:0000:0000:0001
</address>
</client>
</tunnel> CR LF
Figure 18: IPv4 over IPv6 Tunnel Response
In DSTM [DSTM] terminology, the DSTM server is the TSP broker and the
Tunnel Endpoint (TEP) is the tunnel server.
5.4. NAT Traversal Tunnel Request
When a client is capable of both IPv6 over IPv4 and IPv6 over UDP
over IPv4 encapsulation, it can request the broker, by using the
"v6anyv4" tunnel mode, to determine if it is behind a NAT and to send
the appropriate tunnel encapsulation mode as part of the response.
The client can also explicitly request an IPv6 over UDP over IPv4
tunnel by specifying "v6udpv4" in its request.
In the following example, the client informs the broker that it
requests to send keep-alives every 30 seconds. In its response, the
broker accepted the client-suggested keep-alive interval, and the
IPv6 destination address for the keep-alive packets is specified.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
of Presence (PoPs) to offer the service to the customers. IPv6 over
IPv4 encapsulation can be used. If the customers are behind an IPv4
NAT, then IPv6 over UDP-IPv4 encapsulation can be used. TSP can be
used in combination with other techniques.
6.2. Provider Networks with Home/Small Office Customers
In a provider network where IPv4 is dominant, a tunneled
infrastructure can be used to provide IPv6 services to the home/small
office customers, before a full IPv6 native infrastructure is built.
The small networks such as Home/Small offices have a non-upgradable
gateway with NAT. TSP with NAT traversal is used to offer IPv6
connectivity and a prefix to the internal network.
Automation of the prefix assignment and DNS delegation, done by TSP,
is a very important feature for a provider in order to substantially
decrease support costs. The provider can use the same
Authentication, Authorization, and Accounting (AAA) database that is
used to authenticate the IPv4 broadband users. Customers can deploy
home IPv6 networks without any intervention of the provider support
people.
With the NAT discovery function of TSP, providers can use the same
TSP infrastructure for both NAT and non-NAT parts of the network.
6.3. Enterprise Networks
In an enterprise network where IPv4 is dominant, a tunneled
infrastructure can be used to provide IPv6 services to the IPv6
islands (hosts or networks) inside the enterprise, before a full IPv6
native infrastructure is built [RFC4057]. TSP can be used to give
IPv6 connectivity, prefix, and routing for the islands. This gives
the enterprise a fully controlled deployment of IPv6 while
maintaining automation and permanence of the IPv6 assignments to the
islands.
6.4. Wireless Networks
In a wireless network where IPv4 is dominant, hosts and networks move
and change IPv4 address. TSP enables the automatic re-establishment
of the tunnel when the IPv4 address changes.
In a wireless network where IPv6 is dominant, hosts and networks
move. TSP enables the automatic re-establishment of the IPv4 over
IPv6 tunnel.
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RFC 5572 Tunnel Setup Protocol (TSP) February 20106.5. Unmanaged Networks
An unmanaged network is where no network manager or staff is
available to configure network devices [RFC3904]. TSP is
particularly useful in this context where automation of all necessary
information for the IPv6 connectivity is handled by TSP: tunnel
endpoint parameters, prefix assignment, DNS delegation, and routing.
An unmanaged network may (or may not) be behind a NAT. With the NAT
discovery function, TSP works automatically in both cases.
6.6. Mobile Hosts and Mobile Networks
Mobile hosts are common and used. Laptops moving from wireless,
wired in an office, home, etc., are examples. They often have IPv4
connectivity, but not necessarily IPv6. The TSP framework enables
the mobile hosts to have IPv6 connectivity wherever they are, by
having the TSP client send updated information of the new environment
to the TSP server, when a change occurs. Together with NAT discovery
and traversal, the mobile host can always be IPv6 connected wherever
it is.
Mobile here means only the change of IPv4 address. Mobile-IP
mechanisms and fast hand-off take care of additional constraints in
mobile environments.
Mobile networks share the applicability of the mobile hosts.
Moreover, in the TSP framework, they also keep their prefix
assignment and can control the routing. NAT discovery can also be
used.
7. IANA Considerations
A tunnel type registry has been created by IANA. The following
strings are defined in this document:
o "v6v4" for IPv6 in IPv4 encapsulation (using IPv4 protocol 41)
o "v6udpv4" for IPv6 in UDP in IPv4 encapsulation
o "v6anyv4" for IPv6 in IPv4 or IPv6 in UDP in IPv4 encapsulation
o "v4v6" for IPv4 in IPv6 encapsulation
Registration of a new tunnel type can be obtained on a first come,
first served policy [RFC5226]. A new registration should provide a
point of contact, the tunnel type string, and a brief description on
the applicability.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010
IANA assigned 3653 as the TSP port number.
8. Security Considerations
Authentication of the TSP session uses the SASL [RFC4422] framework,
where the authentication mechanism is negotiated between the client
and the server. The framework uses the level of authentication
needed for securing the session, based on the policies.
Static tunnels are created when the TSP negotiation is terminated.
Static tunnels are not open gateways and exhibit less security issues
than automated tunnels. Static IPv6 in IPv4 tunnel security
considerations are described in [RFC4213].
In order to help ensure that the traffic is traceable to its correct
source network, a tunnel server implementation should allow ingress
filtering on the user tunnel [RFC3704].
A customer A behind a NAT can use a large number of (private) IPv4
addresses and/or source ports and request multiple v6udpv4 tunnels.
That would quickly saturate the tunnel server capacity. The tunnel
broker implementation should offer a way to throttle and limit the
number of tunnel established to the same IPv4 address.
9. Conclusion
The Tunnel Setup Protocol (TSP) is applicable in many environments,
such as: providers, enterprises, wireless, unmanaged networks, mobile
hosts, and networks. TSP gives the two tunnel endpoints the ability
to negotiate tunnel parameters, as well as prefix assignment, DNS
delegation and routing in an authenticated session. It also provides
an IPv4 NAT discovery function by using the most effective
encapsulation. It also supports the IPv4 mobility of the nodes.
10. Acknowledgements
This document is the merge of many previous documents about TSP.
Octavio Medina has contributed to an earlier document (IPv4 in IPv6).
Thanks to the following people for comments on improving and
clarifying this document: Pekka Savola, Alan Ford, Jeroen Massar, and
Jean-Francois Tremblay.
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RFC 5572 Tunnel Setup Protocol (TSP) February 2010Appendix B. Error Codes
Error codes are sent as a numeric value followed by a text message
describing the code, similar to SMTP. The codes are sent from the
broker to the client. The currently defined error codes are shown
below. Upon receiving an error, the client will display the
appropriate message to the user.
New error messages may be defined in the future. For
interoperability purpose, the error code range to use should be from
300 to 599.
The reply code 200 is used to inform the client that an action
successfully completed. For example, this reply code is used in
response to an authentication request and a tunnel creation request.
The server may redirect the client to another broker. The details on
how these brokers are known or discovered is beyond the scope of this
document. When a list of tunnel brokers follows the error code as a
referral service, then 1000 is added to the error code.
The predefined values are:
200 Success: Successful operation.
300 Authentication failed: Invalid userid, password, or
authentication mechanism.
301 No more tunnels available: The server has reached its capacity
limit.
302 Unsupported client version: The client version is not supported
by the server.
303 Unsupported tunnel type: The server does not provide the
requested tunnel type.
310 Server side error: Undefined server error.
500 Invalid request format or specified length: The received request
has invalid syntax or is truncated.
501 Invalid IPv4 address: The IPv4 address specified by the client
is invalid.
502 Invalid IPv6 address: The IPv6 address specified by the client
is invalid.
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